The objective of the project is to synthesize Mo-Fe complexes which include some structural features consistent with EXAFS data and which show reactivity toward nitrogenase substrates. Proposed syntheses of the new multinuclear complexes are based on known reaction chemistry of molybdenum dimers. The metal ions in the new complexes will be coordinated by sulfido and thiolate ligands. Previous studies have shown that certain sulfur ligands in molybdenum complexes undergo stoichiometric and catalytic reactions with some nitrogenase substrates. The Mo-Fe complexes have been designed to contain sulfur ligands with similar structural and electronic properties. Reactions of the metal sulfur cores on the new complexes with unsaturated molecules, such as acetylene, isocyanides, nitriles, cyanide, diazo compounds and dinitrogen, will be studied. The studies of these reactive model systems will contribute to the long term objective of understanding the mechanism of nitrogenase.